It is possible that the main title of the report Marfan Syndrome is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.
As Jenny points out, being able to lisp the alphabet song at age two has little to do with 'knowing' the alphabet. And, yes, most children learn the letters by sight and sound in kindergarten, although most are capable of learning this information sooner if diligently taught by parents or others.
The building blocks of language: Babies can learn basic words by age six months due to their exposure to what their parents and siblings might talk about. It was thought that children of that age could understand elements of the sound of their own native language but not connect the sounds to meanings.